The present invention relates to a hydraulic height adjusting device for installing a heavy-weight structure to secure stable horizontal bearing power against a horizontal load of a heavy-weight upper structure. The present invention includes a lower frame which is installed on a top surface of the carrier and is provided with a plurality of receiving portions formed in an upwardly opened shape; and a hydraulic cylinder which is disposed in and engaged to the respective receiving portions of the lower frame, the hydraulic cylinder being moved in a vertical direction to adjust the height of the upper structure, in a state in which an upper end thereof supports the upper structure. The receiving portion is provided with a support guide which is interposed between an inner wall of the receiving portion and the hydraulic cylinder to annually enclose the hydraulic cylinder and thus prevent the hydraulic cylinder from being tilted.